Three of the isozymes of soluble malate dehydrogenase (L-malate:NAD oxidoreductase, E. C. 1.1.1.37) are missing in a spontaneously derived, highly differentiated hepatoma carried in the inbred mouse strain C57L/J. The malate dehydrogenase isozyme pattern of the fetal liver is like the pattern of the hepatoma. An investigation into the genetic and biochemical origin of the soluble malate dehydrogenase isozymes will be undertaken to determine mechanisms which may account for the enzyme deviation in the hepatoma. A developmental study will be undertaken to elucidate the normal isozyme expression in the developing liver. This will be done by following qualitative and quantitative malate dehydrogenase isozyme expression by electrophoresis and spectrophotometric assays of various fetal and newborn stages of development. This will determine the normal expression of soluble malate dehydrogenase isozymes. The soluble isozymes will be purified to protein homogeneity by ammonium sulfate fractionation, Sephadex gel filtration, DEAE cellulose chromatography and preparative electrophoresis. Various catalytic, physical and immunochemical properties of the isozymes will be investigated. This will be done in order to understand the genetic molecular origins of the four soluble malate dehydrogenase isozymes. Since the specific activity of malate dehydrogenase in hepatoma homogenates is less than in liver extracts, the rates of synthesis and degradation (enzyme turnover) will be investigated by density labeling techniques, and by rates of radioactive isotope amino acid incorporation into and loss from soluble malate dehydrogenase specifically isolated by anti-soluble malate dehydrogenase antibody.